The Collaborative International Dictionary of English v.0.48:

Underling \Un"der*ling\, n. [Under + -ling.]
   1. An inferior person or agent; a subordinate; a low-ranking
      employee. --Milton.
      [1913 Webster]

   2. Hence, A mean, sorry fellow. --Milton.
      [1913 Webster]

            The fault, dear Brutus, is not in our stars,
            But in ourselves, that we are underlings. --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

underling
    n 1: an assistant subject to the authority or control of another
         [syn: subordinate, subsidiary, underling, foot
         soldier]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "underling":
   assistant, cog, commonality, commonalty, creature, dependent,
   employee, feudatory, flunky, follower, hanger-on, helper,
   hoi polloi, homager, inferior, junior, lackey, liege, liege man,
   lightweight, lower class, lower orders, masses, minion, myrmidon,
   pawn, peon, poor relation, retainer, right-hand man, scrub,
   second fiddle, secondary, serf, servant, slave, stooge, subaltern,
   subordinate, third stringer, understrapper, vassal, yeoman,
   yes-man